volatile bool running = false;          // Stopwatch running state
volatile unsigned long elapsedTime = 0; // Time in milliseconds
unsigned long previousMillis = 0;       // Stores last update time
unsigned long lastToggleTime = 0;       // For debounce on Start/Stop button
unsigned long lastResetTime = 0;        // For debounce on Reset button

void setup() {
  Serial.begin(9600);                    // Initialize Serial communication
  pinMode(5, INPUT_PULLUP);              // Start/Stop button with internal pull-up
  pinMode(8, INPUT_PULLUP);              // Reset button with internal pull-up

  // Attach interrupts
  attachInterrupt(digitalPinToInterrupt(5), toggleStopwatch, FALLING);
  attachInterrupt(digitalPinToInterrupt(8), resetStopwatch, FALLING);

  Serial.println("Stopwatch Ready");
}

void loop() {
  if (running) {
    unsigned long currentMillis = millis();
    elapsedTime += currentMillis - previousMillis; // Update elapsed time
    previousMillis = currentMillis;

    // Print elapsed time to Serial Monitor
    Serial.print("Time: ");
    Serial.print(elapsedTime / 1000); // Convert milliseconds to seconds
    Serial.println(" s");

    delay(1000); // Update every second
  }
}

void toggleStopwatch() {
  unsigned long currentMillis = millis();
  // Debounce logic for Start/Stop button
  if (currentMillis - lastToggleTime > 200) { // 200 ms debounce time
    running = !running; // Toggle running state
    if (running) {
      previousMillis = millis(); // Reset previousMillis when starting
    }
    lastToggleTime = currentMillis; // Update last toggle time
  }
}

void resetStopwatch() {
  unsigned long currentMillis = millis();
  // Debounce logic for Reset button
  if (currentMillis - lastResetTime > 200) { // 200 ms debounce time
    running = false; // Stop the stopwatch
    elapsedTime = 0; // Reset elapsed time
    Serial.println("Stopwatch Reset");
    lastResetTime = currentMillis; // Update last reset time
  }
}